feat: initial implementation of metadata aggregator

- gRPC service with MusicBrainz provider
- PostgreSQL schema with migrations
- Service layer with database-first caching
- Repository pattern for data access
- YAML configuration support
- Research documentation for 17 music metadata projects

cmd/server/main.go

@@ -0,0 +1,137 @@
+package main
+
+import (
+	"context"
+	"flag"
+	"fmt"
+	"log"
+	"net"
+	"os"
+	"os/signal"
+	"syscall"
+	"time"
+
+	"github.com/jackc/pgx/v5/pgxpool"
+	"google.golang.org/grpc"
+	"google.golang.org/grpc/reflection"
+
+	"github.com/metadata-agregator/internal/config"
+	"github.com/metadata-agregator/internal/provider/musicbrainz"
+	"github.com/metadata-agregator/internal/repository/postgres"
+	"github.com/metadata-agregator/internal/server"
+	"github.com/metadata-agregator/internal/service"
+	metadatav1 "github.com/metadata-agregator/pkg/gen/metadata/v1"
+)
+
+func main() {
+	configPath := flag.String("config", "", "path to config file")
+	flag.Parse()
+
+	cfg, err := config.Load(*configPath)
+	if err != nil {
+		log.Fatalf("failed to load config: %v", err)
+	}
+
+	ctx := context.Background()
+
+	services, cleanup := buildServices(ctx, cfg)
+	defer cleanup()
+
+	addr := fmt.Sprintf(":%d", cfg.Server.Port)
+
+	lis, err := net.Listen("tcp", addr)
+	if err != nil {
+		log.Fatalf("failed to listen: %v", err)
+	}
+
+	grpcServer := grpc.NewServer()
+	metadatav1.RegisterMetadataServiceServer(grpcServer, server.NewMetadataServer(services))
+	reflection.Register(grpcServer)
+
+	go gracefulShutdown(grpcServer)
+
+	log.Printf("gRPC server listening on %s", addr)
+	if err := grpcServer.Serve(lis); err != nil {
+		log.Fatalf("failed to serve: %v", err)
+	}
+}
+
+func buildServices(ctx context.Context, cfg *config.Config) (map[metadatav1.Provider]*service.MetadataService, func()) {
+	mb := musicbrainz.New()
+	services := make(map[metadatav1.Provider]*service.MetadataService)
+
+	dbURL := cfg.Database.DSN()
+	if dbURL == "" {
+		dbURL = os.Getenv("DATABASE_URL")
+	}
+
+	if dbURL == "" {
+		log.Println("no database configured, running in provider-only mode")
+		services[metadatav1.Provider_PROVIDER_MUSICBRAINZ] = service.NewMetadataService(
+			&noopArtistRepo{},
+			&noopAlbumRepo{},
+			&noopTrackRepo{},
+			mb,
+		)
+		return services, func() {}
+	}
+
+	pool, err := connectDB(ctx, dbURL)
+	if err != nil {
+		log.Printf("database connection failed: %v, running in provider-only mode", err)
+		services[metadatav1.Provider_PROVIDER_MUSICBRAINZ] = service.NewMetadataService(
+			&noopArtistRepo{},
+			&noopAlbumRepo{},
+			&noopTrackRepo{},
+			mb,
+		)
+		return services, func() {}
+	}
+
+	artistRepo := postgres.NewArtistRepository(pool)
+	albumRepo := postgres.NewAlbumRepository(pool)
+	trackRepo := postgres.NewTrackRepository(pool)
+
+	services[metadatav1.Provider_PROVIDER_MUSICBRAINZ] = service.NewMetadataService(
+		artistRepo,
+		albumRepo,
+		trackRepo,
+		mb,
+	)
+
+	log.Println("database connected, caching enabled")
+	return services, func() { pool.Close() }
+}
+
+func connectDB(ctx context.Context, dbURL string) (*pgxpool.Pool, error) {
+	ctx, cancel := context.WithTimeout(ctx, 10*time.Second)
+	defer cancel()
+
+	config, err := pgxpool.ParseConfig(dbURL)
+	if err != nil {
+		return nil, err
+	}
+
+	config.MaxConns = 10
+	config.MinConns = 2
+
+	pool, err := pgxpool.NewWithConfig(ctx, config)
+	if err != nil {
+		return nil, err
+	}
+
+	if err := pool.Ping(ctx); err != nil {
+		pool.Close()
+		return nil, err
+	}
+
+	return pool, nil
+}
+
+func gracefulShutdown(server *grpc.Server) {
+	sigCh := make(chan os.Signal, 1)
+	signal.Notify(sigCh, syscall.SIGINT, syscall.SIGTERM)
+	<-sigCh
+	log.Println("shutting down...")
+	server.GracefulStop()
+}

cmd/server/noop_repo.go

@@ -0,0 +1,66 @@
+package main
+
+import (
+	"context"
+
+	"github.com/metadata-agregator/internal/domain"
+	"github.com/metadata-agregator/internal/repository"
+)
+
+type noopArtistRepo struct{}
+
+func (r *noopArtistRepo) GetByID(ctx context.Context, id string) (*domain.Artist, error) {
+	return nil, repository.ErrNotFound
+}
+
+func (r *noopArtistRepo) GetByExternalID(ctx context.Context, source, sourceID string) (*domain.Artist, error) {
+	return nil, repository.ErrNotFound
+}
+
+func (r *noopArtistRepo) Search(ctx context.Context, query string, limit, offset int) (*domain.SearchResult[domain.Artist], error) {
+	return &domain.SearchResult[domain.Artist]{}, nil
+}
+
+func (r *noopArtistRepo) Save(ctx context.Context, artist *domain.Artist) error {
+	return nil
+}
+
+type noopAlbumRepo struct{}
+
+func (r *noopAlbumRepo) GetByID(ctx context.Context, id string) (*domain.Album, error) {
+	return nil, repository.ErrNotFound
+}
+
+func (r *noopAlbumRepo) GetByExternalID(ctx context.Context, source, sourceID string) (*domain.Album, error) {
+	return nil, repository.ErrNotFound
+}
+
+func (r *noopAlbumRepo) GetByArtistID(ctx context.Context, artistID string, limit, offset int) (*domain.SearchResult[domain.Album], error) {
+	return &domain.SearchResult[domain.Album]{}, nil
+}
+
+func (r *noopAlbumRepo) Save(ctx context.Context, album *domain.Album) error {
+	return nil
+}
+
+type noopTrackRepo struct{}
+
+func (r *noopTrackRepo) GetByID(ctx context.Context, id string) (*domain.Track, error) {
+	return nil, repository.ErrNotFound
+}
+
+func (r *noopTrackRepo) GetByExternalID(ctx context.Context, source, sourceID string) (*domain.Track, error) {
+	return nil, repository.ErrNotFound
+}
+
+func (r *noopTrackRepo) GetByISRC(ctx context.Context, isrc string) (*domain.Track, error) {
+	return nil, repository.ErrNotFound
+}
+
+func (r *noopTrackRepo) GetByAlbumID(ctx context.Context, albumID string) ([]domain.Track, error) {
+	return nil, nil
+}
+
+func (r *noopTrackRepo) Save(ctx context.Context, track *domain.Track) error {
+	return nil
+}